1. Field of the Invention
The invention pertains to medical instrumentation systems. More specifically, the invention pertains to urine measuring systems.
2. Description of Related Art
Accurate real time urine output recording is essential to patient management in both the acute and non-acute settings. The closed urine collection system currently in wide use is not automated and relies on a subjective interpretation of urine level relative to printed volumetric markings either on a rigid small volume collection tray or a larger volume collapsible collecting bag. The current system is: error prone, requires arduous physical labor to use, demands repeated potential exposures to biohazordous materials, and is inefficient.
Erroneous urine output value recordings can arise from the antiquated design of the currently widely used closed catheter system leading to improper clinical responses. These errors come most commonly in the form of subjective errors in interpreting urine volumetric markings, arithmetic errors, and neglected readings. These errors in urine output interpretation mean an incorrect patient total body volume assessment causing clinicians to over or under resuscitate their patients which may cause serious complications including renal failure, cardiovascular collapse, or pulmonary edema to name only a few.
Unnecessarily arduous time consuming labor and risk of exposure to biohazardous materials should be minimized as much as possible for medical staff caring for patients. The current urine collection system requires the medical staff member to squat or bend down at the bedside to the low position where the gravity dependent collection bag is stored, which can become quite labor intensive when repeated multiple times throughout the day. The medical staff member is also called upon to do substantial handling of the system as customarily each reading involves the interpreting staff member to pick up the collecting receptacle containing urine in order to raise the volumetric markings on the urine collection receptacle to eye level and the interpreting staff member must also raise the long plastic tube connecting the Foley catheter to the collecting bag to drive any trapped urine from the long plastic tube into the collecting bag. Thus as it now stands, the monitoring of urine output is both physically strenuous and may expose clinical staff to leaked biohazardous material due to frequent daily handling of the urine collecting receptacle and long tube.
Inefficiency is a problem with current systems, and technology providing automation of urine monitoring will bring about a great improvement in this regard. This assertion is supported strongly by a 2002 study by the American Hospital Association that nursing efficiency with non-critical care patients can be increased by as much 12 minutes per patient per day with a digital device to record and calculate hourly and daily urine outputs. With anywhere from 5 to 10 patients per nurse, this amounts to 1 to 2 hours of time saved per day per nurse. And for the critical patients where urine outputs are read and recorded much more frequently, the time savings should be even greater.
In all types of patient monitoring devices the general concept of real time measurement is a critical one. When clinicians create patient care plans the single most important determinant of the plan is the exact state of the patient at that moment in time. If the clinical data lags behind the patient's course, decisions become delayed and patients can suffer dire consequences.
With regards to urine output physiology in the catheterized patient it must be recognized that urine flow with catheterization has two extremes—both very high and very low flow. Depending on conditions, urine flow in a catheterized patient can be as high as 1-2 liters output over 2-3 minutes and as slow as 0-2 cc per hour.
Disposability is vital to a urine monitoring system. Infection control guidelines necessitate that a system for collecting patient biohazardous material such as urine must be disposed of once no longer in use. Any automated system can not forgo this important concept in patient and medical staff safety. A system with even some nondisposable components meant for re-use puts patients and hospital staff at risk of contracting hospital acquired infection.
Versatility of a urine monitoring system comes in the form of the device's ability to function in multiple positions and orientations. Patients are constantly moving and being moved in and out of their beds and rooms. Indwelling bladder catheters in effect bind the patient to the collecting system and any urine monitoring system that must remain in a fixed and rigid orientation binds or anchors the patient to a fixed position. In addition, visiting the bedside will reveal, that in real world use a urine collecting system is not often found hanging in a perfectly upright position and that the collecting bag in fact may be at any angle including entirely horizontal especially during patient transport or bed changing.
Affordability is a necessity when introducing any innovative technology with wide applications in the medical field, as resources are carefully controlled. A system that automatically measures urine output must be composed of inexpensive components to allow for low production and selling costs.
U.S. Pat. No. 6,640,649 by Paz, et al. describes an automated urine monitoring system. The system utilizes a two bag system with one bag collecting urine before passing through a drop generator, which means that this system is unable to handle medium to high urine flow in real time. Also, this system contains expensive components and thus can not practically be entirely disposable, and it requires fixation in the upright position due to the overflow conduit connecting the upper and lower bags.
Both U.S. Pat. No. 5,891,051 by Han, et al. and U.S. Pat. No. 4,448,207 by Parrish describe automated urine monitoring systems utilizing ultrasound to measure the volume of urine accumulated in a rigid collecting chamber, which limits the resolution available. The current cost of ultrasound technology would make disposal prohibitive, and the systems must remain in the fixed upright position for the ultrasound sensor to accurately measure the urine volume in the rigid collecting chamber.
U.S. Pat. No. 4,051,431 by Wurster uses urine as both a conductor of electricity and a dielectric in a capacitor to calculate its flow. This urine measuring apparatus is not designed to be a closed catheter system, but is rather a vessel into which a patient directly voids. U.S. Pat. No. 4,484,582 by Nehrbass uses a rotometer to measure flow in a closed system. Both of these are limited in accuracy at low urine flow. In addition the rotometer of Nehrbass requires a minimum pressure-head to operate which is difficult to achieve at low flow, and for the rotometer system to work, the conduit tube where the rotometer is installed must be completely full with urine which does not occur with low flow.
Jesperson's U.S. Pat. No. 4,343,316 uses an optical sensor to control upper and lower valves in a chamber of fixed volume once the urine level reaches the sensor to calculate urine output. This multi-valve system does not handle either high or low urine flow rates in real time. At high flow the rate of drainage to the collection bag will be stopped, as urine can not flow forward during the time that the chamber is emptied. The monitoring of low flow rate is delayed from real time by the time it takes to fill the chamber.